On paper, the work unit of a CAD software seems to be a simple, almost anecdotal, preference setting. In reality, it is a decision of software architecture that determines whether your plans will remain reliable over the years, collaborators and file exchanges. Between MicroStation and AutoCAD, the philosophy is radically different — and it can literally divide the size of your elements if you do not pay attention to it.
The unit trap in AutoCAD: a tag stuck to a number
In AutoCAD, geometry is basically a sequence of dimensionless numerical coordinates: a line is always recorded as « 0.0 to 10.10 », without any attached unit. Unit setting (UNITS command) only applies a display tag to these raw numbers — it does not convert the existing geometry.
Concretely: an element designed to represent 1 metre is stored below the numerical value « 1 ». If you then change the unit displayed in centimetres, the same « 1 » is reinterpreted as is: your 1 meter element becomes a 1 centimeter element. His real physical grandeur has just been divided by 100, silently, without any warning message.
Even worse, AutoCAD can work in mode « Unitless » (without defined unit at all). The INSUNITS parameter, supposed to allow automatic conversion when inserting blocks or external referencing (Xref), then becomes inoperative: if one of the two files is declared « Unitless », conversion fails and manual scaling — therefore subject to human error — becomes necessary.
MicroStation: a unit of work designed to protect real geometry
MicroStation is based on a reverse logic, and this is precisely what makes it a reliable tool for long-term infrastructure projects. Each file defines a hierarchy of working units consisting of three levels: master unit (Master Unit, e.g. meter), subunit (Sub Unit, e.g. centimeter) and unit of resolution (UOR, Unit of Resolution), the smallest distance the file can send — up to 4,294,967,296 subdivisions.
This architecture means that an element is never a simple number: it is a real physical size, stored as such in the file. Changing the work unit only changes the way this size is expressed on the screen, never its real value. A 1 metre element remains a 1 metre element — it will simply display as « 100 cm » If you switch the master unit to the centimeter. No recovery, no manual verification, no risk of accidental division or multiplication.
Why this difference really counts on the ground
At beCAD, we accompany study offices and infrastructure companies in all French-speaking markets in Europe and Africa — contexts where unit agreements (metres, millimetres, sometimes imperial units on historical projects) constantly intersect between partners, subcontractors and administrations. In this type of multi-stakeholder environment, the robustness of unit management is not a technical detail: this prevents a pipeline network, a building installation or a road route from being delivered on a false scale.
Format DGN native to MicroStation but also from the Bentley Systems software package, directly embeds this definition of work unit in the file, which secures the exchanges between teams and between software of the Bentley Systems platform (OpenRoads Designer, OpenBuildings Designer, OpenPlant...). Conversely, a scale error related to units in a DWG file is one of the recurring causes of costly repeats in the exchange of plans between stakeholders.
Comparison table: 10 key points on unit management
| Criteria | MicroStation | AutoCAD |
|---|---|---|
| Nature of unity | Real work unit integrated into file | Display label applied to a number without dimension |
| Change of unity | Physical size always preserved | Physical size modified according to the selected unit |
| File « Ununited » | Cannot: a work unit is always set | Possible via mode « Unitless » |
| Insertion / external reference (Xref) | Reliable automatic scaling via file unit ratio | Risk of wrong scale according to INSUNITS setting of both files |
| Digital accuracy | Based on UOR, up to 232 subdivisions per master unit | Depends on the decimals displayed, not equivalent to the UOR |
| Traceability of unit | Always visible in the working units settings | Variable INSUNITS system sometimes ignored or misconfigured |
| Multi-country / multi-standard projects | Change of unity without retouching geometry | Often requires a script or manual rescale |
| Native file format | DGN: the work unit is an integral part of the file | DWG: Depends on INSUITS, frequent source of import errors |
| Vigilance curve required | One concept to master: the work unit | Several settings to monitor (UNITS, INSUNITS, insertion scale) |
| Impact on the cost of errors | Risk of structurally excluded scale error | Scale errors frequently cited as causes of recaptures |
migrating well from AutoCAD to MicroStation without losing its benchmarks
Changing the usual work on such a fundamental point as unit management can worry the teams running at AutoCAD. This is why beCAD, Bentley Systems partner, offers dedicated support for migrate fromAutoCAD to MicroStation in complete serenity, and MicroStation training adapted to the level and actual projects of your teams. Our Bentley certified trainers give you the right reflexes to fully exploit the reliability of the work units, from the first projects.
Frequently Asked Questions
Does changing the work unit in MicroStation change the size of my elements?
No. In MicroStation, the physical size of an element is independent of the selected display unit. A 1 metre element remains a 1 metre element, whether displayed in metres, centimetres or millimetres.
Why does my AutoCAD design change scale when I modify the units?
Because AutoCAD stores geometries in the form of non-dimensional numbers. The unit setting is only a display label: it does not recalculate the existing geometry, which may reveal an element at a scale radically different from that desired.
What is the Unit of Resolution in MicroStation?
L?UOR, or unit of resolution, is the smallest distance the MicroStation file can address. It serves as a basis for precision at the Master Unit / Sub Unit hierarchy, with up to 232 possible subdivisions per master unit.
Can AutoCAD work without a defined unit?
Yes, via the mode « Unitless ». This mode prevents reliable automatic conversion when inserting blocks or external references, requiring manual scaling.
Unit management has nothing to do with cosmetic detail: it determines the reliability of your file exchanges, the accuracy of your deliverables and, ultimately, the confidence of your customers. By integrating the work unit into the core of the file architecture, MicroStation structurally eliminates a risk that AutoCAD leaves entirely in the hands of the user. To assess how to secure your projects with Bentley Systems solutions, the beCAD team remains at your disposal.
